1. Field of the Invention
The present invention relates to a transparent substrate with low birefringence, and in particular, relates to a transparent polyimide substrate polyimide having a birefringence below 0.005 for use as a flat panel display substrate.
2. Description of the Related Art
In recent years, development of flat panel displays have trended toward larger and larger sizes, with glass, mainly used as the substrate for fabrication of flat panel displays. Accordingly, as development of flat panel displays trend toward larger and larger sizes, the weight of required glass makes the flat panel display heavier and costly due to increased raw material glass prices. Therefore, in order to meet requirements of lightness and thinness for flat panel displays, plastics is increasingly being substituted for glass, due to the easier processing of plastics and lighter weight.
Plastic substrates have high flexible and winding property, and may be used as the top and bottom substrates of a flexible flat panel display. Flexible flat panel displays utilizing plastic versus glass substrate have advantages such as a lighter weight, thinnest, having better impact resistant, being harder to break, being easier to carry, an ability to display on curved surfaces, an ability to wind and be dressed, and being able to be fabricated roll-to-roll, thus, reducing costs substantially. Therefore, new generation flexible flat panel displays have trended toward utilizing plastic substrates.
At present, the plastic substrate material most commonly used commercially contains polyimide, which has high heat-resistance, high chemical-resistance and high mechanical strength. However, the birefringence of polyimide typically used is too high, usually greater than 0.005. A high birefringence substrate reduces black and white contrast and increases color shift at wide viewing angles.
Therefore, developing a low birefringence polyimide material to be used as a transparent substrate for a flat panel display is desired.